Steam turbines and gas turbines, and also rotary compressors, are counted among thermal turbomachines. These customarily have a rotatably mounted rotor which is enclosed by a stationary housing. The stationary sub-assemblies of a thermal turbomachine are collectively also referred to as a stator. A flow passage for a compressible flow medium, which extends in the axial direction of the turbomachine, is arranged between the rotor and the stator. Rotor blades which are assembled together to form blade groups or blade rows and which project into the flow passage, are customarily fastened on the rotor. In the case of a prime mover, such as a gas turbine, the rotor blades serve for driving the rotor shaft by means of impulse transfer from a hot, pressurized flow medium. The thermal energy of the flow medium, therefore, during its expansion, is converted into mechanical energy which can be used for example for driving an electric generator.
In the case of a rotary compressor which is counted among driven machines, the rotor shaft on the other hand is driven for example by means of an electric motor or internal combustion engine or in another way. The rotor blades which are arranged on the rotor side serve in this case for compressing the flow medium which is in the flow passage and at the same time is heated during this process. That is to say mechanical energy is converted into thermal energy of the flow medium.
The rotating component of a gas turbine, which is also referred to as a rotor, as a rule is subjected to a high mechanical and thermal stress. In particular, the rotor components which form the rotor are heavily stressed as a result of the high temperature of the operating medium and as a result of the forces which act upon the rotor during operation of the gas turbine. In order to nevertheless be able to ensure the operational safety on the one hand and to keep the production costs of the rotor within acceptable limits on the other hand, a number of constructional possibilities were proposed in the past.
A proposed embodiment of the rotor can be realized for example by means of its production from one part. Such a production method, however, is comparatively costly in the manufacturing process. In particular, no prefabrication which is independent of order and no parallel machining of individual parts either is possible so that high production processing times result. Moreover, a larger axial distance between the adjacent rotor blade rings has to be accepted in order to be able to produce with corresponding tools the contours which are required for the fastening of the blades. These manufacturing-dependent, relatively large distances between the rotor blade rings, however, impair the rotor dynamics.
It is furthermore known for example from DE 26 43 886 B1 to also assemble the gas turbine rotor from individual rotor components, wherein the individual rotor components are held together via a tie-bolt. This type of rotor construction can also be used for steam turbines according to CH 344 737. Each rotor component, which is formed as a rotor disk, has an axially extending recess through which the tensioned tie-bolt can extent. By means of threaded nuts which are screwed onto the tie-bolt at the end, this can be tensioned, as a result of which the rotor components, which abut against each other by their end faces, can be clamped to each other. The rotor components are then pressed against each other by the tie-bolt and transmit the rotational forces which act upon them via a so-called Hirth toothing which, disposed on the end face in each case, forms a form-fit between two abutting rotor components.
The rotor of the gas turbine is arranged in the housing of the turbine by means of suitable bearings at the ends. Instead of the threaded nuts, on the casing side more complexly designed components can also be screwed onto the end of the tie-bolt, which in addition to clamping the rotor components also enable further functions, such as the supporting of the rotor in a radial bearing and/or thrust bearing.
During operation of the gas turbine, however, vibrations occur in the rotor, the frequency of which inter alia is dependent upon the spacing of the two thrust bearings, i.e. upon the freely vibrating length of the rotor and especially upon the freely vibrating length of the tie-bolt, in the case of such a type of construction. With increasing overall length of the gas turbine, the freely vibrating length of the tie-bolt also increases, which leads to its natural frequency being shifted to a lower level close to the rotational frequency of the rotor components. This frequency shift can lead to impermissibly high vibration amplitudes during operation of the gas turbine, which can impair the function of the rotor and can lead to damage of the turbine.
In order to counteract this problem, DE 26 43 886 B1 proposes cup rings. The cup rings create an axial connection between rotor disks and tie-bolt in order to reduce its vibrations. The cup rings, however, are not able to be used in the region of a hollow shaft.
Alternatively to this, from NL 50 163 C it is known to seat all the rotor disks of a rotor on a tie-bolt. This type of construction, however, is not installation-friendly. As a specialization of this variant, DE 20 34 088 discloses shells which for maintaining an elastic contact between rotor disks and tie-rod encompass the last-named. Also, this embodiment is comparatively costly during installation.